1. Field of the Invention
The present invention relates to a group key-updating method and device, in which keys of members within a group are updated. More particularly, the present invention relates to a method and device for updating a group key in which when a new member joins a group or an existing member leaves the group, the keys of members in the group can be effectively updated.
2. Description of the Related Art
Traditionally, contents provided to members in a group are encrypted in a server so as not to allow users, except the group members, to utilize the contents. Thus, all the members in the group have an encryption key for decrypting the encrypted contents provided by the server.
Updating of the encryption key of the group members is a very crucial issue. For instance, in the case a new member is joining a group, it is required that the new member have access to only contents after a point in time when the new member join the group. Therefore, when a new member joins the group, a key of existing group members is updated and the new member can share the updated new key with the existing group members.
In addition, in the case an existing member is leaving the group, it is required that the leaving member be refused further access to contents. Thus, a method is needed to update a key used by the group members prior to a point in time when the leaving member has left the group.
When updating a group key is desired, the update can be performed in the following two exemplary implementations.
In the first exemplary implementation, a server calculates the updated key to transmit it to an associated member. The server must calculate a key for all the members requiring the updating of the group key and transmit the calculated key, which can result in an increase in the server's load.
In the second exemplary implementation, a member requiring the updating of the group key calculates the key by themselves and performs a necessary key-updating process. A server then calculates the updated key for only a member who cannot perform a self-update process and transmits the calculated key to the associated member, which results in a relative decrease in the server's load. However, it is difficult for a member requiring the updating of the key to efficiently perform the self-update process.
Accordingly, there is a need for an improved method and device for updating a group key, which can efficiently perform a self-update process.